The effect of the type of the support and the amount of V2O5 loading on the activity of V2O5/gamma -Al2O3 catalyst for the dehydrogenation of isobutane have been investigated. Based on the experimental results of TPR, XRD and ESR spectroscopy, it is suggested that there are strong interactions between vanadia and carrier and that the V4+ species on the surface is the active site of V2O5/gamma -Al2O3 for this reaction.